When the next secretaries of State and Defense take office, their most pressing foreign policy and national security concern won't be traditional threats like global terrorism, rogue states and weapons proliferation. Instead, it will be a domestic economy that is increasingly incapable of sustaining our commitments both at home and abroad.

This is an assessment shared by defense and budget hawks alike. More than two years ago, then-Chairman of the Joint Chiefs of Staff Adm. Mike Mullen said our national debt was the "greatest threat to our national security." Mullen and many others understand that history is littered with great powers that deluded themselves into believing they could live beyond their means indefinitely.

Unfortunately, very few policymakers in Washington are seriously addressing this threat. Yet if the Obama administration and Congress are either unwilling or unable to do the hard work involved in getting our fiscal house in order, they should at least do the easy work. And one easy step that has been ignored for far too long is for the administration to appoint inspectors general, or IGs, to both the departments of State and Defense.

IGs do the vital but unglamorous work of conducting oversight and occasionally taking out the fiscal trash in our massive $3.6 trillion federal government. These public servants have produced big savings for taxpayers across the federal government by rooting out waste and fraud. According to a September 2011 report by the Government Accountability Office, IGs saved taxpayers $43.3 billion in 2009 on a total budget of just $2.3 billion. That's serious money, and a great return on the investment. Over 10 years, that amounts to $433 billion in savings, which is nearly as much as the entire $500 billion 10-year defense sequester. Plus, IGs have uncovered only a portion of the total waste and duplication in the federal government.

Leaving these posts vacant at the departments of State and Defense in a time of war is particularly wasteful and reckless. Without competent IGs, neither the secretaries of Defense nor State will have the tools they need to set priorities and oversee their own agencies.

President Obama's failure to appoint an IG at the State Department for the entirety of his first term is especially egregious. During that time, the State Department's budget has grown by more than 25 percent when adjusted for inflation. The vacancy at the Department of Defense has been for less time (one year), but the defense budget is much larger (about $600 billion) and is rife with waste.

Each year these posts remain unfilled is costing taxpayers billions of dollars. My office has identified nearly $70 billion in "nondefense" defense spending at the DOD, for everything from beef jerky research to studies on Twitter slang to symposiums on extraterrestrial theology that asked, "Did Jesus die for Klingons too?" I believe a competent IG at the DOD could uncover enough waste to fund developing countries or entire departments like NASA, which has a budget of "only" $19 billion.

If Adm. Mullen is correct, our debt is the existential threat of our time. Confronting this threat, I believe, will require extraordinary measures. But the process can start with easy, common-sense steps toward fiscal responsibility. If the administration refuses to take this common-sense step, that may force senators to use all means at their disposal to ensure that these IG posts are filled. Acting IGs are no substitute for permanent IGs that have been nominated by the president and confirmed by the Senate.

My goal is to see more nominations, not fewer, and to have more, not less, debate about the challenges facing our country. I'm convinced that if the next secretaries of Defense and State are going to succeed, they need to have qualified and independent IGs in place who will help make their tenures a success.

Tom Coburn, M.D., is a Republican U.S. senator from Oklahoma.